I. Field
The present invention relates generally to communication, and more specifically to techniques for performing inter-system handoff of a wireless device between two wireless communication networks of different radio access technologies.
II. Background
Wireless communication systems are widely deployed to provide various communication services such as voice, packet data, and so on. These systems may be multiple-access systems capable of supporting multiple users by sharing the available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, and Frequency Division Multiple Access (FDMA) systems. A CDMA system may implement a radio access technology (RAT) such as Wideband CDMA (W-CDMA), cdma2000, and so on. RAT refers to the technology used for over-the-air communication. A TDMA system may implement a RAT such as Global System for Mobile Communications (GSM). W-CDMA and GSM are described in a set of documents from a consortium named “3rd Generation Partnership Project” (3GPP). cdma2000 is described in a set of documents from a consortium named “3rd Generation Partnership Project 2” (3GPP2). 3GPP and 3GPP2 documents are publicly available.
W-CDMA and cdma2000 are third generation (3G) RATs that can provide enhanced services and capabilities (e.g., higher data rates, concurrent voice and data calls, and so on). W-CDMA and cdma2000 utilize different signal processing and controls. Thus, a CDMA system implements either W-CDMA or cdma2000, if at all.
A wireless multi-RAT device (e.g., a dual-mode cellular phone) may have the capability to communicate with both W-CDMA and cdma2000 systems. This may then allow a user/subscriber to obtain services from both W-CDMA and cdma2000 systems and to extend coverage with the same device. For example, the multi-RAT device may initially establish communication with a W-CDMA system and thereafter move out of the coverage area of the W-CDMA system and into the coverage area of a cdma2000 system. In this scenario, it would be desirable to hand off (or hand over) the multi-RAT device from the W-CDMA system to the cdma2000 system in a manner such that the pending communication is minimally interrupted. Unfortunately, no provisions are currently described by 3GPP and 3GPP2 for performing handoff from the W-CDMA system to the cdma2000 system.
There is therefore a need in the art for techniques to perform an inter-system handoff for a multi-RAT device, e.g., from a W-CDMA system to a cdma2000 system.